Chemical vapor deposition apparatus

ABSTRACT

A chemical vapor deposition apparatus is provided. The chemical vapor deposition apparatus includes a susceptor support base and a susceptor, and configured to rotate the susceptor with a rotary shaft, a gap as wide as about 1 mm or more is provided along the boundary between the support base and the perimeter of the susceptor to prevent Ga from forming bridges between the support base and the susceptor during growth of III-V compound semiconductors such as GaN, thereby preventing disturbance of rotation.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Document No.P2001-246177 filed on Aug. 14, 2001, the disclosure of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to a chemical vapor deposition apparatus,especially suitable for application to a metal organic chemical vapordeposition (MOCVD) apparatus.

Devices manufactured by using III-V compound semiconductors, such aslight emitting devices including LEDs and semiconductor lasers, andother devices like communication-purpose high-frequency transistors, areimportant devices constituting hardware infrastructures of the moderncommunication society, together with silicon (Si)-based devices.

III-V compound semiconductor devices, having structures ingeniouslymaking use of hetero junctions of III-V compound semiconductors, take acomplementary part with Si-based devices in regions impossible torealize with Si.

For manufacturing compound semiconductor devices including III-Vcompound semiconductors, excluding simple-structured devices such asMESFET, hetero epitaxial techniques are important techniques. It is noexaggeration to say that hetero epitaxial techniques basically supportthe manufacture of such devices. Molecular beam epitaxy and chemicalvapor deposition, in particular MOCVD, are currently major heteroepitaxial techniques, which have been studied in laboratories since1960s.

MOCVD was bought into practice as an epitaxial growth technique formanufacturing GaAs semiconductor lasers. Currently, an MOCVD apparatusenabling epitaxial growth on a number of substrates simultaneously iscommercially available. In terms of componential techniques of themulti-substrate MOCVD apparatus, there are various types. Regarding thesusceptor configuration, there are a barrel type and a pancake type. Interms of the gas flow mode, there are a high-flow-rate horizontal type,high-revolution type, vertical down-flow type, and so on. In terms ofthe substrate-supporting mode, there are schemes of putting substratesabove the gas flow (face-down) or putting substrates under the gas flow(face-up). Regarding heating there are a RF induction heating type,electrical resistance heating type, lamp heating type, and so on. Thesecomponential techniques are combined variously to make up various typesof MOCVD apparatuses.

Conventional MOCVD apparatuses for epitaxial growth of III-V compoundsemiconductors uses gallium (Ga), aluminum (Al) or indium (In) as agroup III element and arsenic (As) or phosphorus (P) as a group Velement, and the growth temperature was 800° C. at most. On the otherhand, there is a recent demand for an MOCVD apparatus capable ofepitaxially growing GaN compound semiconductors using ammonia (NH₃) as asource material.

A MOCVD apparatus for GaN semiconductors is configured to invitereaction of a group III organic metal compound and ammonia (NH₃) at atemperature around 1100° C. to grow a single-crystal thin film on asapphire or SiC substrate. Concerning the single-crystal thin film, gascomposition and growth conditions for growing high quality crystals wereacademically reported and known. However, MOCVD apparatuses forrealizing optimized gas composition and growth conditions for obtaininghigh quality crystals have been modified after individual technicalresearches, and almost none of their actual improvements are known.Among some known MOCVD apparatuses, there are some proposals directed tothe structure of the reaction tube (for example, Japanese PatentLaid-open Publications Nos. JP-H02-288665A, JP-H04-94719 A andJP-H11-12085). Even with these techniques, it has been difficult tomanufacture semiconductors of long-lasting good crystal qualities underacceptable reproducibility because of various entangled factors.

SUMMARY OF THE INVENTION

The present invention generally relates to a chemical vapor depositionapparatus, particularly a metal organic chemical vapor deposition(MOCVD). The present invention provides a chemical vapor depositionapparatus optimized for obtaining quality high crystals by epitaxialgrowth of compound semiconductors, and especially GaN compoundsemiconductors.

The Inventor continued vigorous studies to overcome the above-discussedproblems involved in the prior art techniques. The contents of thestudies are introduced hereunder.

A chemical vapor deposition apparatus typically includes a susceptor,and a support base holding the susceptor, as shown in FIG. 1. Thesusceptor is designed to rotate on its own axis relative to the supportbase. In FIG. 1, reference numeral 1 denotes the support base, 2 is thesusceptor, 3 is a substrate, 5 is a rotation axis for rotation of thesusceptor, and 6 is a heater. The heater 6 is put in the support base 1in some designs. The support base 1 may be configured to rotate in somedesigns. Rotation of the susceptor 2 enhances the uniformity ofthickness of the film deposited on the substrate 3.

After repeated use of the apparatus, decomposition products accumulateas sediments 4 on the susceptor 2 and the support base 1, and sediments4 accumulating along the boundary between the support base 1 and thesusceptor 2 under relative movements disturbs the rotational movements.It has been recognized that a serious problem occurs especially whengrowing gallium nitride semiconductors. For growth of a gallium nitridesemiconductor, the substrate surface is cleaned with a flow of hydrogenfor 10 minutes at 1100° C., for example. In this hot cleaning process,nitrides accumulated on the susceptor 2 in the preceding manufacturingprocess decompose, and metallic gallium remains in form of smalldroplets on the surface. Liquid gallium near the boundary between thesusceptor 2 and the support base 1 makes small balls by surface tension,and invites bridging at the boundary between the susceptor 2 and thesupport base 1. When ammonia gas is supplied for the next growth step,liquid metallic gallium nitridized, and solid of gallium nitride againgrows along the boundary as shown by numeral 41. The GaN solid havingintruded into the boundary seriously disturbs rotation of the susceptor2, and may ultimately cause mechanical destruction. Therefore, it willbe effective to separate the susceptor 2 and the support base 1 by adistance wide enough to prevent formation of bridges by metallicgallium.

The support base including the susceptor may be configured to inclinefrom the upstream to the downstream of the gas flow to increase the flowrate of the gas. This will contributes to uniforming the film inthickness. In vapor deposition of nitrides, however, accumulatednitrides may cause the above-explained undesirable problem following theprocess of changing to liquid metallic gallium, moving along theinclined surface into the gap between the susceptor and the supportbase, making bridges of metallic gallium therebetween, and forming thesolid in the next step supplying ammonia. Therefore, to prevent thisphenomenon, it will be effective to make grooves of ridges and furrowson the support base and thereby block the flow of metallic galliumdroplets beyond the grooves.

Known techniques use the mechanism as show in FIG. 2 to rotate thesusceptor 2, in which the support base 1 and susceptors 21 have formedannular grooves equal in diameter and hold carbon balls 91 in thegrooves. Gears 93 are formed at end portions of the susceptors 21 anddriven by external stationary gears 8 to realize rotational movementsreduced in friction. However, since the susceptors 21 and the supportbase 1 are not integral, the susceptors 21 may jump and disengage undervibrations when the rotation speed increases. Especially in a growthapparatus for growth of nitride compound semiconductors at hightemperatures, in which SiC-based materials having rough surfaces areoften used, improvement of the susceptor structure has been longed for.Therefore, it will be effective to provide an independent bearingmechanism between each susceptor 21 and the support base 1.

There is a type of mechanism for rotating the susceptor, which cannotrotate the center axis of the susceptor directly. A typical way forcoping with it uses a gear on the circumference of the susceptor todrive the gear with an external gear. In this case, however, if thetemperature is raised high for growth like the growth apparatus ofnitride semiconductors, it is necessary to cope with the problem ofrelative positional offset by thermal expansion and the problem of anincrease of the frictional force. Therefore, if new system is employed,which includes a mechanism located on the circumference of one ring ofsusceptors or bearings to resist against wind pressure and an inlet tubeintroducing a gas flow into the mechanism, it is possible to preventirregular torque by slipping. Thus, the new system is effective againstdestruction of rotating members by relative positional offset andagainst an increase of the frictional force.

As a way of heating the susceptor, there is a lamp-heated system thathave actually been employed in a nitride compound semiconductor growthapparatus of a normal pressure type (Japanese Patent Laid-openPublication No. JP-H11-12085A). Among apparatuses of a reduced pressuretype, there are only a few examples using a heating lamp. Especiallyamong growth apparatuses for nitride compound semiconductors, noapparatuses have heretofore employed lamp-heated systems. However, thisis made possible by employing a system in which the lamp house itselfforms a part of the depressurizing container.

With regard to a mechanism for rotating a large-scaled rotationalsusceptor or support base, some apparatuses employ a system not holdingthe center axis of rotation. For example, as shown in FIG. 3, in case adonut-shaped carbon susceptor 2 is located to encircle the support base1 made of a rotatable quartz disk having a center axis, and thedonut-type carbon susceptor 2 alone is heated, it is impossible tointegrally fix the support base 1 and the susceptor 2 because thesupport base 1 made of quarts and the susceptor 2 made of carbon aredifferent in thermal expansion coefficient. Therefore, their relativepositions vary with temperature. In another configuration as shown inFIG. 4, in which a plurality of susceptors 21 attached on a largerotatable support base 1 having a center axis of rotation is rotatedboth about its own axis and together with the support base 1 by astationary gear 8 located to encircle the them together, the stationarygear 8 around them must be isotropically expanded (contracted) inresponse to the thermal expansion (contraction) of the rotationalsupport base 1 while maintaining it center stationary when thetemperature rises (or decreases). If not, gears will fail to biteproperly and will break ultimately. Reaction apparatuses such as growthapparatuses for nitride compound semiconductors, which are required towork at growth temperatures as high as 1100° C., are subjected to largethermal expansion. Therefore, unless the outer-circumferentialstationary gear 8 is expanded while keeping its center axis stationary,the outer-circumferential stationary gear 8 cannot engage accuratelywith the gears 90 of the susceptors 21 attached on the rotatable disk,and will become unable to drive the susceptors 21. Therefore, it isindispensable to use a structure for maintaining the center point at aconstant position upon isotropic deformation like thermal expansion of amember whose center cannot be fixed physically. As a structure for thispurpose, it is useful to provide connection rods at some positions onthe member having rotation symmetry to extend equally in length andequally in angle from diametric lines passing their positions, and toconnect the opposite ends of the connection rods to a member independentfrom the member having rotation symmetry. Thus, the center point of themember is maintained constant even upon isotropic deformation thereof.

For immediately stopping a drive mechanism (motor) in the rotatingsystem for driving the center axis directly upon any extraordinaryfriction on the part of the rotating member, a slip mechanism wastypically used heretofore between the drive mechanism and the rotationaxis. This system certainly stops the rotating member by slipping.However, it is impossible to know the occurrence of the extraordinaryphenomenon at that moment. Taking it into account, it is effective todevelop this mechanism by introducing a rotary encoder between therotational member and a slipping member or a torsionally deformablemember to know any irregularity by processing the rotation output of therotary encoder and the rotation output from the drive mechanism with acomparator and an information processing device, so as to stop the drivemechanism and generate an alarm signal.

As an alternative of the mechanism for stopping the drive mechanism, itis also effective to equip the drive mechanism itself, and an air-driventype mechanism will be effective for this purpose.

For MOCVD of III-V compound semiconductors, a plurality of sourcematerial gases are used. It has been acknowledged that confluence pipesmust be properly arranged to bring source material gases controlled inflow rate into confluence with the main tube communicating with thereactor. For example, if two pipes merge to collide head-on with eachother as shown in FIG. 5, then the gases from two pipes collide andinterfere each other, vibrations produced thereby makes it impossible toproperty control the flow rate. Therefore, for bringing a plurality ofpipes containing source material gases into confluence, it has beenconfirmed effective to employ a structure in which the pipes do notconfront head-on, or the pipes merge at points offset by at least adistance corresponding to the diameter of the pipe.

The present invention has been made based upon the above-explainedresearches by the Inventor.

In an embodiment, the first aspect of the invention is a chemical vapordeposition apparatus that includes a gap that is provided along theboundary between a support base and the perimeter of a rotationalsusceptor supported on the support base.

To reliably prevent the bridging, the width of the gap along theboundary between the support base and the perimeter of the rotatablesusceptor is preferably determined to be equal to or wider than about0.5 mm, or more preferably determined to be equal to or wider than about1 mm. On the other hand, if the gap is excessively wide, material gaseswill readily intrude in the gap and will accumulate on its sidewalls.Therefore, to prevent it, the width of the gap is preferably determinednot to exceed about 3 mm, or more preferably determined not to exceedabout 2 mm. Similarly, depth of the gap is preferably determined to beequal to or deeper than about 1 mm, or more preferably determined to beequal to or deeper than about 2 mm. On the other hand, depth of the gapis preferably determined to be shallower than or equal to about 4 mm, ormore preferably determined to be shallower than or equal to about 3 mm.

The second aspect of the invention in an embodiment is a chemical vapordeposition apparatus including a support base, and a rotationalsusceptor attached to the support base with an inclination relative tothe direction of gravity, wherein grooves of ridges and furrows areformed on the support base so that a decomposition product of a gas isaccumulated in the grooves.

The third aspect of the invention in an embodiment is a chemical vapordeposition including; a support base; and a susceptor rotating mechanismincluding a bearing mechanism fixed to the support base and having arotation transmission gear, and a susceptor fixed to one of rotatingrotational members of the bearing to rotate therewith.

To incorporate a pair of opposed rotational members via balls, thebearing mechanism typically has a bearing structure in which the pair ofrotational members are concentrically threaded so that, once bothmembers are joined and relatively rotated beyond the threadingengagement, the ridges of the threads function as disturbances againstdisengagement of the members and hold them integrally.

The fourth aspect of the invention in an embodiment is a chemical vapordeposition apparatus including a support base; and a susceptor rotatingmechanism having a bearing mechanism fixed to the support base and asusceptor fixed to one of rotational members of the bearing to rotatetherewith, wherein one of the opposed rotational members includes amechanical portion for receiving wind pressure, and a mechanism forguiding a gas flow to the mechanical portion.

The fifth aspect of the invention in an embodiment is a chemical vapordeposition apparatus having an external heating means and a reactionchamber that are separate chambers separated by a partition plate,wherein a communication passage is provided near a gas discharge outletto equalize the external heating means and the reaction chamber inpressure.

The sixth aspect of the invention in an embodiment is a chemical vapordeposition apparatus including a structural body having a rotationsymmetry and not fixed in position of its center point; and a structurefor keeping the position of the center point against isotropicdeformation such as thermal expansion of the structural body.

To keep the position of the center point, a plurality of connection rodsare provided to extend from a plurality of points on the member havingthe rotation symmetry in directions equally offset from the diametricdirections, and connected to a member independent from the member havingthe rotation symmetry at equally distant positions from the memberhaving the rotation symmetry.

The seventh aspect of the invention in an embodiment is a chemical vapordeposition apparatus including a rotary encoder as a mechanism fordetaching a drive force upon extraordinary torque caused by a failure ofa substrate rotting mechanism; a slip or deformable connector to copewith extraordinary torque, and a mechanism for stopping a driverdepending upon a result of comparison between the rotation signal of therotary encoder and the rotation signal of the driver.

The eighth aspect of the invention in an embodiment is a chemical vapordeposition including an air driver directly connected to a rotary shaftas a mechanism for detaching a drive force upon extraordinary torquecaused by a failure of a substrate rotating mechanism so that the airdriver slips upon generation of extraordinary torque.

The ninth aspect of the invention in an embodiment is a chemical vapordeposition includes that a plurality of pipes containing source materialgases merge a unit pipe structure at positions preventing head-oncollision of the pipes, or at positions distant by at least the diameterof the pipe.

The invention is suitable for application to metal organic chemicalvapor deposition apparatus among various types of chemical vapordeposition apparatuses. Especially, it is suitable for use in growth ofIII-V nitride semiconductors containing a group III element such asgallium (Ga), aluminum (Al), boron (B) and indium (In), and a group Velement, such as of nitrogen (N), phosphorus (P) and arsenic (As), andthe like.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view showing the substantial part of aconventional chemical vapor deposition apparatus.

FIG. 2 is a cross-sectional view showing the substantial part of anotherconventional chemical vapor deposition apparatus.

FIG. 3 is a plan view showing a particular part of still anotherconventional chemical vapor deposition apparatus and a correspondingpart of a chemical vapor deposition apparatus according to an embodimentof the present invention.

FIG. 4 is a plan view showing a particular part of yet anotherconventional chemical vapor deposition apparatus and a correspondingpart of a chemical vapor deposition apparatus according to an embodimentof the present invention.

FIG. 5 is a schematic diagram showing a pipe system of a conventionalchemical vapor deposition apparatus.

FIG. 6 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 7 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 8 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 9 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 10 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 11 is a schematic diagram showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

FIG. 12 is a pipe system in a chemical vapor deposition apparatusaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to a chemical vapor depositionapparatus, particularly suitable for a metal organic chemical vapordeposition. Some embodiments of the invention will now be explainedbelow in detail with reference to the drawings.

FIG. 6 shows configuration of a reactor in a chemical vapor depositionapparatus according to the first embodiment of the invention. In FIG. 6,reference numeral 1 denotes a support base made of a quarts material.Numeral 2 denotes a SiC-coated susceptor, and numeral 3 denotes asapphire substrate. Numeral 5 denotes a rotary shaft for rotating thesusceptor 2, 6 is a heater, and 7 is a reactor made of stainless steel.The process for crystal growth of GaN is explained below. Firstintroduced is hydrogen gas into the reactor 7. Then, the reactor 7 isheated to about 1100° C. for about 15 minutes to clean the surface ofthe sapphire substrate. Then, the temperature is lowered to about 550°C., and ammonia and trimethyl gallium (TMG) is supplied to depositamorphous GaN up to a thickness around 30 nm. Thereafter, the supply ofTMG is interrupted, and while ammonia and hydrogen are supplied, thetemperature is raised to about 1100° C. to crystallize GaN accumulatedunder a low temperature. Subsequently, TMG is again supplied toaccumulate single crystal GaN on the micro seed crystals. The process ofthese sequential steps is known.

After completion of the crystal growth, the substrate is removed, and anew sapphire substrate is set on the same position for the next growthround. The condition at the start of the second growth round isdifferent from that of the initial growth round in that GaN existsaround the susceptor 2 or on the support base 1. This GaN sedimentdecomposes in hydrogen in the process of cleaning the substrate surfaceas the first step of the second growth round because of a hightemperature, and makes micro metal droplets of Ga. The sediment is shownat 4 in FIG. 1. FIG. 1 shows configuration of the susceptor and itsperipheral members in a conventional chemical vapor depositionapparatus. The rotational susceptor 2 and the support base 1 aretypically formed not to interpose a gap within the extent of the currentmachining accuracy. Actually, however, there inevitably exists the gapof approximately 0.1 mm. Metallic gallium produced may exist above thegap, i.e. along the boundary between the susceptor 2 and the supportbase 1, and it appeared to intrude into the gap experientially. Althoughits mechanism is not clear, it will be possible to suppose that microdroplets join and become a certain size, and intrude into the gap bysurface tension. This is shown at 41 in FIG. 4.

In the next process of supplying ammonia to form gallium nitride, the Gametal is nitridized by ammonia, and again forms GaN. Responsively,simultaneously with the solidification, it expands in volume andproduces a strong frictional force that disturbs rotation. Ultimately,it may lead to destruction of the mechanisms. In view of suchexperiential phenomenon, the first embodiment of the invention adds animprovement as shown in FIG. 6. That is, against the common knowledge ofsizing them not to produce a substantial space between them, theembodiment makes a space around 1 mm or more between them, and the gapis dug down to a depth equal to or deeper than 2 mm. This is shown at 11in FIG. 6. In this configuration, even when the GaN accumulated on thesupport base 1 changes to Ga metal, it does not form bridges to thesusceptor 2, and therefore do not intrude into the gap 11. The amount ofdeposition on sidewalls of the gap 11 was small because the sourcematerial gases do not reach there. Therefore, the susceptor 2 could beused for much more rounds of crystal growth before it needs replacement,and the productivity was enhanced accordingly.

In a lateral type apparatus in which source material gases areintroduced horizontally and flow in parallel with the substrate, thesusceptor is inclined by raising the downstream side thereof for thepurpose of uniforming the growth thickness of the film. In case ofgrowth of III-V nitride semiconductors, bridging over the boundarybetween the susceptor 2 and the support base 1 by gallium metal becomesmore serious because droplets of gallium slip down the slope. To improvethe apparatus in this respect, the second embodiment of the inventionemploys the improvement shown in FIG. 7. That is, the support base 1 hasformed grooves 12 of ridges and furrows. Thus, gallium metal drops inthe grooves 12, or downward flows of the gallium metal are interruptedby the grooves 12. Therefore, gallium metal is unlikely to accumulatebetween the susceptor 2 and the support base 1. As a result, theapparatus could be used for much more rounds of the growth process, andthe productivity thereof was enhanced.

FIG. 2 shows one of known techniques for rotating the substrate. Thesupport base 1 and the susceptors 21 have formed annular grooves, and aplurality of carbon balls 91 are held in the grooves to support thesusceptors rotationally. For transmission of the rotational force, agear 93 is formed at an end of each susceptor 21 and engages with anexternal stationary gear 8. When the rotary shaft 5 rotates the supportbase 1, the susceptors 21 rotate about their own axes. Although this isan excellent mechanism, it is insufficient depending upon its materials.In case the apparatus is intended for growth of GaN, for example, whichneeds a high growth temperature, the support base 1 and the susceptors21 are made of SiC or SiC-coated carbon. These are very hard materials,and the machining accuracy and the surface condition of the grooves andthe gears are worse than those made of carbon. Moreover, since sapphireballs are used instead of carbon balls 91, the apparatus is insufficientin lubricity, and a larger frictional force is produced during rotation.As the rotating speed increases, large vibrations will occur. In extremecases, disharmony occurs among rotatable members, the susceptors 21 willaccidentally disengage eventually. Therefore, for growth of GaN compoundsemiconductors, the apparatus needs a structure reliably preventingaccidental disengagement. It has been confirmed that this problem can beovercome by inserting an independent bearing mechanism between thesupport base 1 and the susceptors 2. FIG. 8 shows the third embodimentof the invention directed to this improvement. Here is shown only a partthereof necessary for explanation of this system. In FIG. 8, numeral 21refers to a susceptor, and 90, 91 and 92 denote components of thebearing, which are made of SIC or nitride-based new ceramics. Numeral 93denotes a gear formed on one of complementary members of the bearing,which is connected to the external stationary gear 8. The mechanismincorporating the bearing mechanism and preventing accidentaldisengagement upon vibrations is realized by male and female screws 94.For assembling the mechanism, sapphire balls 91 are first put in thegroove of the other complementary member 92 of the bearing fixed to thesupport base 1, and the other rotational member 90 is next put thereonand rotated to fasten the screws 94. Thus, the members 90 and 92 engagedeeper and deeper beyond the engagement of the screws 94, and becomefree as illustrated. Thereafter, the complementary members of thebearing do not disengage unless the upper member is lifted against thegravity and rotated oppositely. A gear 93 is associated with thebearing, and rotates under engagement with the external fixed gear 8.Other than the above-explained mechanism, there are various types ofmechanisms for incorporating the bearing. If a retainer is used toreduce interference between balls, more stable rotation will be ensured.

FIG. 9 shows a chemical vapor deposition apparatus according to thefourth embodiment of the invention. Here is shown another examplerelated to the way of rotating the bearing shown in FIG. 8. In FIG. 9,numeral 95 denotes a wind pressure receiver that receives a windpressure from a gas inlet 81 and converts the energy to a rotating forcefor the bearing. This mechanism is advantageous in releasingextraordinary resistance to the bearing by slipping and being therebyfreed from destruction.

FIG. 10 shows a chemical vapor deposition apparatus according to thefifth embodiment of the invention, which employs lamp-aided heating fromabove as a heating means. In FIG. 10, numeral 71 denotes a lamp housethat is an integral part of the pressure container. Numeral 72 denotes ahalogen lamp, 73 is a cooling gas inlet path for cooling the lamp, 74 isa pressure through path opening to a downstream position of the reactor,and 75 is a partitioning plate for separating the gas flow-in path fromthe lamp portion. The partitioning plate 75 is a transparent quartzplate having a thickness of about 5 mm to about 10 mm. Since thepressure through path 74 merges the exhaust gas, the exhaust gas mayaccidentally flow back toward the lamp upon a change in reactionpressure. To prevent it, inactive gas for the cooling purpose iscontinuously supplied from the cooling gas inlet path 73. Since thepressure through path 74 renders the lamp side and the substrate sideapproximately equal in air pressure, the partitioning plate 75 may bethin. This configuration makes it possible to employ the lamp-aidedheating method under a reduced pressure.

FIG. 3 shows a system for rotating a large-sized donut-shaped rotationalsusceptor 2 supported on the circumferential surface of the support base1 and rotated when the support base 1 rotates. The donut-type susceptor2 is employed in apparatuses configured to blow out source materialgases from the center in radial directions. The support base 1 istypically made of quartz, and the donut-type susceptor 2 is SiC-coatedcarbon. The support base 1 is not heated, but the susceptor 2 is heatedto 1100° C. for example. Therefore, these members cannot be fixed, andthe susceptor 2 is supported only by contact with the circumferentialsurface of the support base 1. Alternatively, a guide in the radialdirection may be provided, but the susceptor 2 cannot be united with thesupport base 1. Therefore, thermal expansion and contraction inrepetitive heating and cooling cause a deviation of the center positionof the susceptor 2. To prevent the positional deviation, the sixthembodiment of the invention connects them with quartz connection rods100. The connection rods 100 each have fixed points on the support base1 and on the susceptor 2. The line connecting the fixed points of eachconnection rod 100 is offset from the diametric line passing the fixedpoint on the support base 1 by a certain angle, such as 45 degrees. Inoperation, when the donut-type susceptor 2 expand due to a rise of thetemperature, the inner diameter of the susceptor 2 also expands. Then,in case of FIG. 3, each connection rod 100 rotates the susceptor 2 in adirection reducing the angle from the diametric direction, making use ofthe expansion force of the susceptor 2. Thus, the donut-type susceptor 2can keep the center point upon isotropic deformation thereof.

FIG. 4 shows a chemical vapor deposition apparatus according to theseventh embodiment of the invention, taken as another example that mustexpand and contract while keeping the center position. In FIG. 4,numeral 21 denotes a susceptor set in a bearing mechanism. Numeral 8denotes an external stationary gear. Numeral 93 denotes cogs of the gear90 in engagement of the cogs of the external stationary gear 8. Inoperation, when the support base 1 rotates about its center point, thesusceptor 21 set on the bearing mechanism is rotated about its owncenter and together with the support base 1 by engagement of the cogs 93of the gear 90. When the temperature rises, both the support base 1 andthe external stationary gear 8 expand by thermal expansion. If theexternal stationary gear 8 expands under no restriction, i.e. under nomeans keeping the center point, the engagement becomes tight on one handand loose on the other hand. Such uniform gear engagement invitescollision of cogs and destruction thereof. The connection rods 100,however, assures smooth rotation by permitting the stationary gear 8 toexpand while keeping the center point by the same principle.

Regarding countermeasures against extraordinary rotation, almost notechniques have been taught. FIG. 11 shows a chemical vapor depositionaccording to the eighth embodiment of the invention, improved in thepower transmission system of the rotating system to cope with irregularoperation of the apparatus. In FIG. 11, numeral 110 denotes a rotaryencoder, numeral 111 denotes a connector slidable or torsionallydeformable under large torque, and numeral 112 denotes a driver such asa stepping motor. Numeral 113 is a comparator of electrical signals, andnumeral 114 is an information processing device. This system operates asexplained below. Let an extraordinary torque be caused by anirregularity occur in the rotating system of the support base 1. Oncethe connector 111 slips or twists, rotation signals from the rotaryencoder 110 and rotation signals from the driver 112 disagree. Thecomparator 113 detects the disagreement, converts it to a digitalsignal, and delivers it to the information processing device 114.Responsively, the information processing device 114 analyzes theirregularity, interrupts the driver 112 and generates an alarm signal115. In this manner, destruction of the reactor can be prevented.

As the pipe arrangement for supplying source material gases to thereactor, chemical vapor deposition apparatuses typically let carrier gasflow in the main pipe, and connect source material gas pipes to the mainpipe. FIG. 5 shows a conventional layout of pipes. For example, 116denotes the main pipe that is connected to the reactor at position I. InFIG. 5, the main pipe is labeled A, and source materials gas pipes arelabeled B through H. The portion of A, B is the pipe arrangement of aunit for one source material, the portion of C, D is that for two sourcematerials, and the portion of E through H is that for four sourcematerials. Typically, source material gas pipes are gathered andconnected substantially at one point as shown in FIG. 5 because, if themain pipe has a large pipe resistance, the pressure will differ amongdifferent positions of the pipe system, and will cause undesirableproblems upon switching gases. However, this arrangement of pipes hasbeen confirmed through actual use thereof to involve the problemexplained below. That is, when the flow rate of source materials gasesincreases, vibrations occurred in the flows of source materials gases.This is because that the gas pressure from one of opposed pipes, C,influences the other of the opposed pipes, D; the flow rate controller(mass flow controller, MFC) of the pipe D gives a feedback control; itsresult influences the control of the counter part pipe C; and repetitionof this cycle causes vibrations or chaotic behaviors of the gas flows.The vibrations can be controlled to a certain extent by adjusting thetime constant of the flow rate controllers. However, it has beenconfirmed that the phenomenon of vibrations can be essentially removedby using the pipe arrangement shown in FIG. 12 that illustrates theninth embodiment of the invention. That is, it is important that aplurality of pipes to be joined do not meet head-on, or their mergingpoints are distant from each other by a distance with which the changein pressure by entrance of each gas is reduced to a negligible level.From this point of view, it has been confirmed that nearest two mergingpoints of pipes should be distant at least by the interval equal to ormore than the pipe diameter.

Heretofore, some specific embodiments of the invention have beenexplained. However, the invention is not limited to these embodiments,but contemplates other various modifications based upon the technicalconcept of the present invention. For example, the first embodimentshown in FIG. 6 can be extended to a system intended for processing aplurality of substrates simultaneously. Further, although thoseembodiments have been explained as being of a face-up type, they can bemodified to a face-down type. The concept of keeping the center point bythe use of connection rods 100 is also usable for holding the bearingmechanism in the apparatus, for example. Moreover, it is applicable toall mechanisms having difficulties in fixing the center point.

As described above, according to the first aspect of the invention in anembodiment, since the gap is provided between the rotational susceptorand the support base, the apparatus is freed from disturbance ofrotation caused by bridging of these members by deposits, and isoperative for more rounds of crystal growth process. Thus, themanufacturing capability by the apparatus is enhanced.

According to the second aspect of the invention in an embodiment,grooves by ridges and furrows on the support base removes disturbance ofrotation caused by undesirable flows of deposits to the boundary withthe susceptor even in inclined reactor devices. Here again, theapparatus is operative for more rounds of crystal growth process, andenhanced in manufacturing capability.

According to the third and fourth aspects of the invention in anembodiment, the use of the independent, new bearing mechanism in therotation system ensures stable rotation of the substrate, enhances theproduction yield and improves the manufacturing capability.

According to the fifth aspect of the invention in an embodiment, the useof the pressure through path in the lamp-aided heating type apparatusmakes it possible to employ the lamp-aided heating also inpressure-reduced systems to manufacture substrates with high-qualityfilms grown thereon.

According to the sixth aspect of the invention in an embodiment, in asystem including members subjected to isotropic deformation such asthermal expansion, center positions of those members can be keptconstant to ensure their stable rotational movements and enhance thecapability of the apparatus.

According to the seventh aspect of the invention in an embodiment usinga combination of the rotary encoder and the connector that can slip ortwist, it is possible to stop the driver immediately upon any irregularrotation and generate an alarm signal to prevent any damage to theapparatus.

According to the eighth aspect of the invention in an embodimentincluding the air-aided driver directly connected to the rotary shaft,it is possible to stop the driver immediately upon any irregularrotation to prevent any damage to the apparatus.

According to the ninth aspect of the invention in an embodimentemploying the pipe arrangement for chemical vapor deposition apparatusesin which source material gas pipes do not meet head-on when they merge,high-quality crystal growth is possible without vibrations by gas flows.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A chemical vapor deposition apparatus comprising: a donut-shapedcarbon susceptor supported on a quartz central support base and rotatedwhen the support base rotates, having a rotational symmetry and notfixed in position of its center point; and a plurality of connectionrods made of quartz for maintaining a position of a center point againstisotropic deformation of the susceptor, provided to extend from aplurality of points on the susceptor in directions equally offset from adiametric direction, and connected to the support base at equallydistant positions from the susceptor, each of the connection rods havinga fixed point on the support base and the susceptor, respectively, eachof the connection rods rotating the susceptor in a direction reducing anangle from the diametric direction, making use of an expansion force ofthe susceptor, when the susceptor expands due to an increase intemperature.
 2. The chemical vapor deposition apparatus according toclaim 1, wherein the apparatus includes a metal organic chemical vapordeposition apparatus.